1. Field of Invention
The invention relates to a method for making cyanoacrylates.
2. Description of Related Art
Monomer and polymer adhesives are both used in industrial (including household) and medical applications. Included among these adhesives are 1,1-disubstituted ethylene monomers and polymers, such as .alpha.-cyanoacrylates. Since the discovery of the adhesive properties of such monomers and polymers, they have found wide use due to the speed with which they cure, the strength of the resulting bond formed, and their relative ease of use. These characteristics have made .alpha.-cyanoacrylate adhesives the primary choice for numerous applications such as bonding plastics, rubbers, glass, metals, wood, and, more recently, biological tissues.
Medical applications of 1,1-disubstituted ethylene adhesive compositions, such as .alpha.-cyanoacrylate compositions, include use as an alternate and an adjunct to surgical sutures and staples in wound closure as well as for covering and protecting surface wounds such as lacerations, abrasions, burns, stomatitis, sores, and other surface wounds. When an adhesive is applied, it is usually applied in its monomeric form, and the resultant polymerization gives rise to the desired adhesive bond.
U.S. Pat. No. 5,624,669 to Leung et al. describes a process for making cyanoacrylates. In the method, .alpha.-cyanoacrylates are prepared by condensing a cyanoacetate and either formaldehyde or paraformaldehyde in the presence of a catalyst at a molar ratio of 0.5-1.5:1 to obtain a condensate; depolymerizing the condensation reaction mixture either directly or after removal of the condensation catalyst to yield crude cyanoacrylate; and distilling the crude cyanoacrylate to form a high purity cyanoacrylate. In order to prepare a particular .alpha.-cyanoacrylate, the '669 patent discloses making a corresponding cyanoacetate by esterifying cyanoacetic acid with the corresponding alcohol or by transesterifying an alkyl cyanoacetate with the corresponding alcohol before the cyanoacetate undergoes the condensation reaction with the formaldehyde or paraformaldehyde.
U.S. Pat. No. 4,364,876 to Kimura et al. describes reaction conditions for forming .alpha.-cyanoacrylates by the method described in the '669 patent.
U.S. Pat. No. 2,721,858 to Joyner et al. and U.S. Pat. No. 2,763,677 to Jeremias et al. also describe reaction conditions for forming .alpha.-cyanoacrylates from the corresponding cyanoacetate.
As used herein the terms "corresponding" or "corresponds" with reference to a cyanoacetate and an .alpha.-cyanoacrylate means that the same R group is attached to oxygen of the carboxyl group in the two compounds. Thus, methylcyanoacetate corresponds to methyl .alpha.-cyanoacrylate. The term "corresponding alcohol," as used herein, refers to an alcohol having the same R group attached to the hydroxyl group as the corresponding cyanoacetate or .alpha.-cyanoacrylate has attached to the oxygen of the carboxy group. Thus, methyl alcohol corresponds to methylcyanoacetate and to methyl .alpha.-cyanoacrylate.
In all of the above mentioned references, the cyanoacetate that undergoes the condensation reaction corresponds to the .alpha.-cyanoacrylate that is obtained.
U.S. Pat. No. 5,637,752 to Nakamura et al. describes reaction conditions for the transesterification of a lower alkyl cyanoacetate with an alcohol to form a higher alkyl cyanoacetate.
SU 726,086 describes a process for producing .alpha.-cyanoacrylates by reacting ethyl .alpha.-cyanoacrylate monomer with excess alcohol in the presence of an acid or metal chloride catalyst. The process is simplified and polymerization of the final product is prevented by conducting the transesterification reaction at 100-140.degree. C. in the presence of sulfuric or para-toluene sulfonic acid or zinc chloride catalyst.
U.S. Pat. No. 2,756,251 to Joyner et al. describes a method for depolymerizing polymeric .alpha.-cyanoacrylates.